The External Anatomy of Spiders 



a part of the epigynum, they are sometimes visible in mounted 

 specimens in which the epigynum has been rendered transparent 

 (Fig. 132). 



Care should be taken not to mistake the glands of the sperma- 

 thecae, which are often dark and show through the body-wall, 

 for the openings of the spermathecae. (See account of these glands 

 in the following chapter.) A secondary function of the epigynum, 

 as an ovipositor, is discussed later. 



An example of a comparatively simple epigynum is that of 

 Pirata montanus (Fig. 131, a); this is a nearly plain plate, with 

 the two openings of the sperm- 

 athecae near the posterior lateral 

 corners. A somewhat more 

 complicated form is illustrated 

 by the epigynum of Trabea au- 

 rantiaca (Fig. 131, b); in this 

 the plate is depressed or fur- 

 rowed longitudinally, and the 

 depressed area is divided by a 

 ridge-like elevation, which di- 

 vides the depression into two 

 furrows or channels, each of 

 which leads to the opening of 

 the spermatheca of the corre- 

 sponding side; this ridge-like 

 elevation has been termed the 

 guide by Chamberlin ('04), as 

 its function "seems clearly to 

 be that of a guide to the male 

 embolus, controlling the course of the latter and facilitating its 

 entrance to the spermatheca." In many cases the guide extends 

 laterally on each side at its posterior end; this is true to a slight 

 extent in the epigynum of Trabea, but more markedly so in that 

 of many species of Lycosa, where the lateral expansions often 

 conceal the openings of the spermathecae, as in the epigynum 

 of Lycosa ptkei (Fig. 131, c). In some epigyna the posterior 

 portion of the median part of the guide and the anterior edge of 

 the lateral extensions of it are extended horizontally in plate-like 

 expansions, these are termed, by Chamberlin ('08) the lateral 

 plates or ala- of the guide. 



131 



Fig. 132. 



EPIGYNUM OF THERIDIOX 

 DIFFERENS 

 1, surface view 2, view when made trans- 

 parent *, openings of the spermathcae 

 s. spermathecae z, tube leading 

 from the spermatheca to the 

 vagina (alter Emerton) 



